(1) Field of the Invention
This invention relates to a radiotherapy planning system for making a treatment plan, such as determining an irradiation field shape, in advance of treating disease such as cancer with radiation.
(2) Description of the Related Art
In treating disease such as cancer with radiation, the diseased part must be irradiated properly. For this purpose, a radiotherapy planning system is used to acquire images of and around the diseased part by means of an X-ray CT apparatus and a fluoroscopic apparatus, and to determine an irradiation field shape coinciding with an outline of an image of the diseased part appearing in an image acquired.
Such a radiotherapy planning system often includes a CT simulator and an X-ray simulator. The CT simulator has an X-ray CT apparatus as a main component thereof, while the X-ray simulator has an X-ray TV apparatus as a main component thereof. These simulators have certain additional functions, respectively. First, CT radiography is carried out using the CT simulator to acquire a plurality of sectional images. These sectional images are combined to reproduce a three-dimensional image, and then an oblique image (transmitted image seen from one direction) is produced therefrom. Alternatively, CR images which are fluoroscopic images are photographed by linearly moving a CT detector. These simulation images are displayed to identify a diseased part to be treated.
Next, an irradiating angle is determined from sectional images of a wide region including the diseased part or a transmitted image, seen from a particular direction, produced from a three-dimensional image obtained by combining the sectional images. A transmitted image seen from the irradiating angle is displayed. Then, the operator determines a shape of an irradiation field on the image displayed, and sets an isocenter to the irradiation field. Further, a position corresponding to the isocenter is marked on the patient's surface (skin surface).
Subsequently, the patient is positioned relative to the X-ray simulator by using the mark on the skin surface as a reference, so that the mark coincides with the isocenter of the X-ray simulator. An X-ray irradiating angle corresponding to the irradiating angle determined as above is set to the X-ray simulator, and an image is photographed on a film through radiography for use as a reference photograph for collation.
Further, the patient is positioned relative to a radiation treating apparatus by using the mark on the skin surface as a reference, so that the mark coincides with the isocenter of the treating apparatus. An irradiating angle is set to the irradiating angle determined as above, and film radiography is carried out by emitting radiation. This radiation film image is collated with the above X-ray film image acting as the reference photograph to confirm that the patient has been positioned according to plan.
After this is confirmed, radiotherapy is performed for the diseased part by actually emitting radiation from the radiation treating apparatus.
However, the conventional radiotherapy planning system has a drawback of not always assuring a treatment plan made for irradiating a diseased part with an appropriate irradiation field shape.
That is, in the conventional system, an oblique image or the like produced from sectional images acquired from the CT simulator is a still picture, and therefore cannot accurately reflect in the treatment plan the movement of internal organs and the like due to respiration and other functions. Further, fluoroscopic images are conventionally acquired with the X-ray simulator using an image intensifier. The fluoroscopic images acquired are distorted by curvature of the X-ray incidence surface. When an irradiation field shape is verified on a fluoroscopic image, the field shape fails to exhibit a reliable geometrical conformity to the actual diseased part.